JP5139877B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming technique for forming an image on a recording medium.

  As a technique for correcting density unevenness, Patent Document 1 detects density unevenness of a plurality of recording elements at a predetermined timing during image recording, and based on the detection result, a drive signal applied to the recording head is obtained. Techniques for adjustment are disclosed.

Further, in Patent Document 2, based on the result of comparing the test pattern with the image obtained by repeating the recording of the image and the intermittent conveyance of the recording medium by the data obtained by mixing the test pattern data with the image data, A technique for correcting the conveyance amount of the recording medium is disclosed.
Japanese Patent Laid-Open No. 02-286341 JP 2006-218774 A

  However, in the technique disclosed in Patent Document 1, image data is corrected when the number of recorded sheets reaches a predetermined value or when the inactive period reaches a predetermined value. Therefore, it is impossible to correct the density unevenness that occurs automatically. For this reason, image data cannot be corrected in real time.

  Further, in the technique disclosed in Patent Document 2, since recording is performed while mixing a test pattern with a recorded image, density unevenness due to an error in the conveyance amount can be suppressed, but an image of a test pattern is added to an image to be printed. Since it is necessary to add, it may become a factor which deteriorates appearance.

  Accordingly, an object of the present invention is to form an image with higher image quality by correcting density unevenness in real time.

In order to solve the above-described problems, the image forming apparatus of the present invention has the following configuration. That is, in an image forming apparatus in which an image is formed on the recording medium by causing the recording head to perform recording scanning N times (N is an integer of 2 or more) with respect to the same area on the recording medium. A recording data generating means for generating corresponding recording data; a recording means for recording the image on the recording medium based on the recording data generated by the recording data generating means; and the recording head. together with the recording scan of the k-th by the recording means (k is an integer satisfying 2 ≦ k ≦ N), the recording state of the image recorded on the recording medium by the recording scan to (k-1) th by the recording means a detecting means for detecting that was detected by the detection unit (k-1) based on the recording state until times, at least one of the generation of the print data corresponding to the k-th print scan A control means for controlling the image processing, the.

  According to the present invention, it is possible to form an image with higher image quality by correcting density unevenness in real time.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the prior art and the present invention will be described in detail with reference to the drawings.

<Conventional technology>
As an example of an apparatus using a print head provided with a plurality of printing elements, an ink jet printing apparatus using a print head provided with a plurality of ink discharge ports has been known. In an inkjet printing apparatus, the size and position of dots formed with ink vary due to variations in the ink discharge amount and direction, and density unevenness may occur in a printed image. In particular, in a serial type printing apparatus that prints by scanning an inkjet head in a direction different from the arrangement direction of a plurality of print media (for example, a direction orthogonal to the print media), the density unevenness due to the above-described variation is a streak. It appears as unevenness in the shape and appears in the printed image. For this reason, the quality of the printed image has been reduced.

  In addition, in order to correct such density unevenness, in the case of the ink jet printing method, one line of image data (dot pattern) after halftone processing such as binarization processing is discharged from a plurality of different discharge ports. A method of forming with ink is proposed. This can be realized, for example, by supplementing one line of image data with a plurality of scans (scans or passes) by feeding paper less than the width of the print head. This method is generally called a multi-pass printing (or recording) method.

  The multipass printing method includes a method using a mask pattern and a method of dividing the density of an input image to be printed in multiple values into a plurality of scans and generating print data for each of the divided ones. is there.

  In the method of dividing a pass using a mask pattern, in order to divide print data once generated into a plurality of prints, a mask pattern corresponding to the pass is prepared in advance, and the mask pattern and the generated print data are It was printed by taking the logical product. This mask pattern is determined in advance so that all generated data can be cut off by printing a plurality of times. In order to perform multi-pass pass division, the mask pattern is determined as 100% printable dots, and the printable dots are determined for each pass. It is set to be equal to the whole area when the logical sum of possible dots is taken. For this reason, the mask pattern itself is selected to be as random as possible in order to avoid interference with the halftone process.

  In addition, the present inventors have proposed a method of performing pass division by performing density division on an input image to be printed in accordance with scanning. This method determines the density ratio at which the input image to be printed is printed corresponding to each scanning motion, and density-divides the input image to be printed according to the division ratio determined according to the print density ratio for each scan. In this method, halftone processing is performed to generate print data. In either case of the mask pattern method or the density division method, the input image to be printed is divided into a plurality of scans for printing. The multipass printing operation will be described below.

  FIG. 13 is a diagram illustrating a conventional procedure for dividing an input image into four passes. The horizontal axis is the density of the input image, and the vertical axis is the output density on the print medium. The output density with respect to the input density is not linear, and usually draws a curve that swells in the positive direction of the vertical axis. However, in the conventional density division, basically, when dividing into four passes, the input density data Is equally divided into four. That is, the input density division ratios k1, k2, k3, and k4 in the first to fourth passes are divided so that k1: k2: k3: k4 = 1: 1: 1: 1 as shown in FIG. To do. In either case of the mask pattern method or the density division method, the input image to be printed is divided into a plurality of scans and printed.

  FIG. 17 is a diagram showing a conventional example of multipass printing. Here, an example of 4-pass printing in which an inkjet head is scanned four times to form an image on the print medium 310 will be described.

  The inkjet head 300 is divided into four regions 300a, 300b, 300c, and 300d, and a plurality of nozzles are arranged in the vertical direction in each region. The region 300a is the lowermost region of the inkjet head 300, and the region 300b is a region adjacent to the upper side of the region 300a. The region 300c is a region adjacent above the region 300b, and the region 300d is a region adjacent above the region 300c. The regions 300a to 300d are formed by equally dividing the region of the inkjet head 300 into four as described above.

  After the inkjet head 300 scans the print medium 310, the printer repeats printing by moving the print medium 310 upward with respect to the inkjet head 300 by a paper feed mechanism.

  FIG. 17A shows the first pass scanning for the area 310-1. First, among the print data to be printed in the area 310-1 of the print medium 310, the print data to be printed in the first pass is transmitted to the lower quarter area 300a of the inkjet head 300, and the print medium 310 is moved in the left direction. Scan (or right). Thus, the first pass printing is performed on the area 310-1 of the print medium 310 by the nozzles arranged in the area 300a. In the first pass printing, print data is not transmitted to the nozzles arranged in the regions 300b, 300c, and 300d of the inkjet head 300, and printing is not performed in the region of the print medium 310.

  When this printing process is completed, the paper is fed by the length of 1/4 of the inkjet head 300 (that is, the width in the nozzle arrangement direction in the region 300a) with the print medium 310 on the upper side.

  FIG. 17B shows the second pass scanning for the area 310-1. The ink jet head 300 is at a position indicated by a solid line with respect to the print medium 310 during the second pass scanning of the area 310-1. Note that the inkjet head 300 was at a position 300-1 illustrated by a broken line with respect to the print medium 310 during the first pass scanning, which is the first pass before the second pass.

  First, print data to be printed in the first pass among print data to be printed in the area 310-2 of the print medium 310 is transmitted to the area 300a of the inkjet head 300, and the area 310-2 of the print medium 310 is left. Scan in the direction (or right). Thus, the first pass printing is performed on the area 310-2 of the print medium 310 by the nozzles arranged in the area 300a.

  In addition, print data to be printed in the second pass among the print data to be printed in the area 310-1 of the print medium 310 is transmitted to the area 300b of the inkjet head 300, and the area 310-1 of the print medium 310 is left. Scan in the direction (or right). Thus, the second pass printing is performed on the area 310-3 of the print medium 310 by the nozzles arranged in the area 300b. Since the areas 300c and 300d of the inkjet head 300 are not yet in the print area, the print data is not transmitted to the area of the print medium 310 and printing is not performed.

  When these printing processes are completed, the paper is fed by the length of ¼ of the inkjet head 300 (that is, the width of the region 300a in the nozzle arrangement direction) upward.

  FIG. 17C shows the third pass scanning for the region 310-1. The ink jet head 300 is at a position illustrated by a solid line with respect to the print medium 310 during the third pass scanning with respect to the area 310-1. Note that the inkjet head 300 was at a position 300-1 illustrated by a broken line with respect to the print medium 310 at the time of scanning of the second pass, which is the pass before the third pass. In addition, the inkjet head 300 was at the position 300-2 indicated by the broken line with respect to the print medium 310 during the first pass scanning, which is the second pass before the third pass.

  First, the print data to be printed in the first pass among the print data to be printed in the area 310-3 of the print medium 310 is transmitted to the area 300a of the inkjet head 300, and the area 310-3 of the print medium 310 is left. Scan in the direction (or right). Thus, the first pass printing is performed on the area 310-3 of the print medium 310 by the nozzles arranged in the area 300a.

  Also, the print data to be printed in the second pass among the print data to be printed in the area 310-2 of the print medium 310 is transmitted to the area 300b of the inkjet head 300, and the area 310-2 of the print medium 310 is left. Scan in the direction (or right). Thus, the second pass printing is performed on the area 310-2 of the print medium 310 by the nozzles arranged in the area 300b.

  Further, the print data to be printed in the third pass among the print data to be printed in the area 310-1 of the print medium 310 is transmitted to the area 300c of the inkjet head 300, and the area 310-1 of the print medium 310 is left. Scan in the direction (or right). Thus, the third pass printing is performed on the area 310-1 of the print medium 310 by the nozzles arranged in the area 300c. Since the area 300d of the inkjet head 300 has not yet entered the print area, the print data is not transmitted to the area of the print medium 310 and printing is not performed.

  When these printing processes are completed, the paper is fed by the length of ¼ of the inkjet head 300 (that is, the width of the region 300a in the nozzle arrangement direction) upward.

  FIG. 17D shows the fourth pass scanning for the region 310-1. The ink jet head 300 is located at a position illustrated by a solid line with respect to the print medium 310 during the fourth pass scanning with respect to the area 310-1. The inkjet head 300 was at a position 300-1 indicated by a broken line with respect to the print medium 310 at the time of the third pass scanning, which is the first pass before the fourth pass. In addition, the inkjet head 300 was at the position 300-2 indicated by the broken line with respect to the print medium 310 during the second pass scanning, which is the second pass before the fourth pass. Furthermore, the inkjet head 300 was at a position 300-3 indicated by a broken line with respect to the print medium 310 at the time of the first pass scanning three times before the fourth pass.

  First, the print data to be printed in the first pass among the print data to be printed on the area 310-4 of the print medium 310 is transmitted to the area 300a of the inkjet head 300, and the area 310-4 of the print medium 310 is left. Scan in the direction (or right). Thus, the first pass printing is performed on the area 310-4 of the print medium 310 by the nozzles arranged in the area 300a.

  Also, the print data to be printed in the second pass among the print data to be printed in the area 310-3 of the print medium 310 is transmitted to the area 300b of the inkjet head 300, and the area 310-3 of the print medium 310 is left. Scan in the direction (or right). Thus, the second pass printing is performed on the area 310-3 of the print medium 310 by the nozzles arranged in the area 300b.

  In addition, print data to be printed in the third pass among the print data to be printed in the area 310-2 of the print medium 310 is transmitted to the area 300c of the inkjet head 300, and the area 310-2 of the print medium 310 is left. Scan in the direction (or right). Thus, the third pass printing is performed on the area 310-2 of the print medium 310 by the nozzles arranged in the area 300c.

  Further, the print data to be printed in the fourth pass among the print data to be printed in the area 310-1 of the print medium 310 is transmitted to the area 300d of the inkjet head 300, and the area 310-1 of the print medium 310 is left. Scan in the direction (or right). Accordingly, the fourth pass printing is performed on the area 310-1 of the print medium 310 by the nozzles arranged in the area 300d.

  When these printing processes are completed, the printing processes in the first to fourth passes are performed by the area 300a, the area 300b, the area 300c, and the area 300d of the inkjet head 300, respectively. Completes all image formation.

  After the fourth pass scanning for the area 310-1 is completed, the print medium 310 is fed upward by the length of 1/4 of the inkjet head 300 (that is, the width of the area 300a in the nozzle arrangement direction). Thereafter, printing by the scanning of the inkjet head 300 and paper feeding are sequentially repeated to form an image on the print medium 310.

  In this way, to reduce density unevenness such as streaks and unevenness due to paper feed errors in the drive unit and nozzle head variations, the area on the print medium is divided into multiple scans and printed on each scan. Conventionally, a multi-pass printing method in which data is divided and printed has been performed.

  By performing multi-pass printing, density unevenness such as streaky unevenness due to variations in the amount of conveyance of the print medium 310 by the drive unit and variations in the nozzles of the inkjet head (such as variations in the discharge amount and the discharge direction) It has been possible to reduce it to some extent. However, while the demand for higher print image quality is increasing, the conventional multi-pass printing method alone solves the problems in the above-mentioned printer by reducing the size of the print droplets and increasing the print resolution. It is difficult to suppress density unevenness.

  14 and 15 are diagrams showing the positions of dots formed in each pass in the conventional example. An aspect in which density unevenness such as streaky unevenness due to variations in the conveyance amount of the print medium by the drive unit and variations in the nozzle characteristics of the ink jet head (e.g., variations in ejection amount and ejection direction) will be described. However, in order to clearly explain density unevenness caused by variations in the transport amount of the print medium by the drive unit and nozzle characteristics of the inkjet head (such as variations in the discharge amount and the discharge direction), there are some differences from actual printing. .

  FIG. 14 shows dots ejected to ideal positions when printing at a certain density is performed by four-pass printing. A circle is a print dot, and the number in the circle is a pass number indicating which of the first to fourth passes is printed. Here, the division coefficient divided into each pass will be described assuming that the print ratio of each pass is equal to 0.25. Further, in order to clearly show density unevenness, it is assumed that the odd lines of the print lines are printed in the first and third passes, and the even lines are printed in the second and fourth passes (unlike actual printing). ). Assuming that there is no variation in ejection characteristics due to the inkjet head (such as variation in ejection amount or ejection direction) and that there is no variation in the conveyance amount of the print medium by the printer drive unit, as shown in FIG. The images are formed with uniform density.

  However, when variations in image quality such as the ejection characteristics of the inkjet head and the conveyance amount of the printing medium are added, as shown in FIG. 15, the arrangement of the ink dots is deviated from the ideal state. The concentration will not be uniform. In FIG. 15, the transport amount of the print medium after the first pass printing and the third pass printing is slightly increased, the transport amount of the print medium after the second pass printing is slightly decreased, and the discharge direction is further decreased. It is in a state with variations. As a result, ideally, the dots should be arranged equally as shown in FIG. 14, while the second line and the third line are close to each other, while between the first line and the second line, In addition, the third line and the fourth line are separated from each other, and density unevenness occurs in this portion. In order to suppress such density unevenness, the following embodiments can be employed in the present invention.

<First Embodiment>
FIG. 1 is a block diagram showing a functional configuration of a printer 10 according to an embodiment of the present invention.

  In this embodiment, the printer 10 is an inkjet printer, and includes a CPU 100, a ROM 110, a RAM 120, a USB device interface 130, and a USB host interface 140. In addition, the printer 10 includes an image processing unit 150, a print control unit 160, a drive control unit 170, and a printer engine unit 180.

  The CPU 100 is a central processing unit that controls the printer 10, and the ROM 110 stores programs and table data for the CPU 100. The RAM 120 is a memory that stores variables and data.

  The USB device interface 130 is an interface (I / F) that receives data from the personal computer (PC) 20. The USB host interface 140 is an interface (I / F) that receives data from an electronic device such as the digital camera 30. In this embodiment, it is assumed that the personal computer 20 is connected to the USB device interface 130 and the digital camera 30 is connected to the USB host interface 140.

  The image processing unit 150 performs processing such as color conversion and binarization on a multi-valued image input from an electronic device such as the digital camera 30, and the print control unit 160 performs binarization processing on the image processing unit 150. The recorded data is transmitted to a printer engine unit 180, which will be described later, and printing control is performed. The printer engine unit 180 includes an inkjet head, a paper feed mechanism, and a carriage feed mechanism, and prints a gradation image on the print medium 200 based on a control signal from the print control unit 160. The drive control unit 170 controls a drive unit (for example, the number of rotations of a motor) of the printer engine unit 180 such as a paper feed mechanism and a carriage feed mechanism.

  Here, it is assumed that an image photographed by the digital camera 30 is directly transmitted to the printer 10 for printing without going through the personal computer 20. First, for a print medium (not shown) set in the printer engine unit 180, information on the print medium is read by a sensor (not shown) for detecting the type, and the CPU 100 determines the type of the print medium. The Various sensors for detecting the type of print medium have been proposed. For example, light of a specific wavelength is projected onto the print medium to read the reflected light, and the reflected light is compared with a plurality of wavelength samples stored in advance. Thus, a method for discriminating the print medium can be adopted.

  Image data captured by the digital camera 30 is stored in the memory 31 in the digital camera 30 as a JPEG image. The digital camera 30 is connected to the USB host interface 140 of the printer 10 with a connection cable. The captured image stored in the memory 31 of the digital camera 30 is temporarily stored in the RAM 120 in the printer 10 via the USB host interface 140. Since the image data received from the digital camera 30 is a JPEG image, the CPU 100 is used to decompress the compressed image into image data and store the image data in the RAM 120. Based on the image data stored in the RAM 120, print data for printing with the inkjet head of the printer engine unit 180 is generated. The image data stored in the RAM 120 is subjected to color conversion processing, binarization processing, and the like by the image processing unit 150 to be converted into print data (dot data), and is further divided into passes so as to correspond to multi-pass printing. Details of the processing procedure in the image processing unit 150 will be described later.

  The data converted into the print data and divided into passes is transmitted to the print control unit 160, and is transmitted to the inkjet head of the printer engine unit 180 in accordance with the drive order of the inkjet head. Then, in synchronization with the drive control unit 170 and the printer engine unit 180, the print control unit 160 generates ejection pulses, ejects ink droplets, and forms an image on a print medium (not shown).

  In this embodiment, the binarization process is performed by the image processing unit 150. However, since it is only necessary to reduce the gradation to print the input image, the present invention is not limited to the binarization. For example, not only when there are two levels of ink density and ink droplet size, but also when there are three levels, N (N is an integer of 2 or more) value for data reduction. It is included.

  In the present embodiment, a sensor (not shown) disposed in the printer engine unit 180 detects the presence or absence of a print medium set in the printer 10, and the print medium is based on information detected by the CPU 100 using the sensor. The type of was determined. However, the user may select the type of print medium by operating the printer 10 or the digital camera 30.

  2A to 2C are views showing the arrangement of the print medium 200 and the carriage 210. FIG.

  As shown in FIG. 2A, the carriage 210 is equipped with an inkjet head 220 and a sensor 230, and can scan in either the left or right direction. The inkjet head 220 has four color heads, a cyan head 220c, a magenta head 220m, a yellow head 220y, and a black head 220bk, and a plurality of nozzles for each color. The sensor 230 is a color sensor that detects the RGB printing state on the printing medium 200. The sensor 230 is disposed adjacent to a position preceding the inkjet head 220 (downstream in the main scanning direction X) with respect to the direction in which the printing scanning movement is performed (main scanning direction X). That is, the sensor 230 moves in synchronization with the inkjet head 220. In this embodiment, a color sensor that detects the RGB printing state is used as the sensor 230, but a CMY complementary color sensor, a monochrome sensor, or the like may be used.

  The carriage 210 performs printing by ejecting ink droplets from the nozzles of the inkjet heads 220 of the respective colors when the print medium 200 is scanned in the main scanning direction X. When printing for one scan is completed, the print medium 200 is conveyed in the sub-scanning direction Y by the printer engine unit 180 (see FIG. 1), and the print medium 200 is set at the position of the next scan.

  In the present embodiment, since the multi-pass printing is performed by scanning the print area a plurality of times and performing printing, the single conveyance amount of the print medium 200 is smaller than the nozzle width of the inkjet head 220. In other words, in this embodiment, a quarter of the nozzle width of the inkjet head 220 is conveyed for each scan of the carriage 210.

  As shown in FIG. 2A, when the main scanning direction X (the direction in which the printing scanning motion is performed) is the right direction in the drawing, the sensor 230 is controlled by the inkjet head 220 with respect to the main scanning direction X. Will also be located in the preceding position. For this reason, when performing multi-pass printing, the print state up to the print scan (that is, the (n-1) th pass) one time before the print scan of interest (the nth pass) is detected during the scan. be able to. The printing state actually changes depending on the ejection characteristics of the inkjet head 220 (variations in the ejection amount and ejection direction of ink), the variation in the conveyance amount of the printing medium 200 by the printer engine unit 180 (see FIG. 1), and the like. The state printed on the top. Accordingly, it is possible to correct density unevenness in real time during scanning of the carriage 210 based on the detection result detected by the sensor 230. Details will be described later in this embodiment.

  On the other hand, as shown in FIG. 2B, the sensor 230 has the inkjet head 220 with respect to the main scanning direction X when the main scanning direction X (direction in which the printing scanning motion is performed) is the right direction in the drawing. It can also be arranged at a subsequent position. In this case, it is not possible to detect the printing state up to the (n-1) th pass when generating the recording data of the target pass (assumed to be the nth pass). That is, the printing state up to the nth pass is detected. For this reason, density unevenness is not corrected in real time during scanning, but the output of the sensor 230 is held and corrected for one scan. Details will be described later in the fourth embodiment.

  Further, in the case where the forming process on the recording medium is performed in both the forward path and the backward path of the reciprocating scanning movement, as shown in FIG. 2C, the ink jet head is moved in the direction in which the sensor 230 performs the printing scanning movement. It may be placed at both the 220 preceding and following positions. The sensor 230 disposed on the left side (the above-described subsequent position) of the inkjet head 220 is referred to as a sensor 231, and the sensor 230 disposed on the right side (the above-described preceding position) of the inkjet head 220 is referred to as a sensor 232. In this case, in the case of scanning in which the main scanning direction X is the right direction, the printing state is detected by the sensor 231, and in the case of scanning in which the main scanning direction X is the left direction, the printing state is detected by the sensor 232. To detect. Accordingly, when performing bidirectional printing, the same control can be performed even when scanning in either the left or right direction.

  FIG. 3 is a block diagram illustrating a functional configuration of the image forming apparatus according to the first embodiment. The image forming apparatus reciprocates the inkjet head 220 a plurality of times with respect to the same area on the print medium 200. In the reciprocating scanning motion, dot formation processing is performed on the print medium 200 in one of the reciprocating scanning motion, and the multipass processing is performed on the other side of the reciprocating scanning motion to move to the original position. A gradation image is formed.

  First, the input image 320 is converted from an RGB signal into a CMY signal 335 (cyan signal 335c, magenta signal 335m, and yellow signal 335y) to be printed by the printer 10 (see FIG. 1) by the color conversion unit 330. The The RGB signals detected from the sensor 340 that detects the print state are converted into CMY signals 355 (cyan signal 355c, magenta signal 355m, and yellow signal 355y) by the color conversion unit 350. The color conversion unit 350 performs color conversion to the CMY signal 355 based on, for example, the color filter characteristics of the RGB signal of the sensor 340, the characteristics of the light source applied to the detection area of the sensor 340, and the characteristics of the ink to be printed. Do.

  Then, the CMY signal 335 converted by the color conversion unit 330 and the CMY signal 355 converted by the color conversion unit 350 are converted into a print data generation unit 370 (cyan print data generation unit 370c, magenta print data generation unit 370m, yellow color). The data is input to the print data generation unit 370y). The print data generation unit 370 corrects the print data in synchronization with the printing by the printer engine unit 180 based on the printing state detected by the sensor 230.

  The print data generation unit 370 performs binarization in order to perform printing with an inkjet head, and generates print data for each recording scanning motion. After the print data generating unit 370 generates the print data of the inkjet head, it is input to the print control unit 380 (cyan print control unit 380c, magenta print control unit 380m, yellow print control unit 380y) for each color. The print control unit 380 performs print control on the printer engine unit 180 (see FIG. 1) such as an ink jet head based on the print data with reduced gradation, and forms an image on the print medium.

  FIG. 4 is a block diagram illustrating a functional configuration of the print data generation unit 370 according to the first embodiment. Here, the functional configuration of one of the cyan print data generation unit 370c, the magenta print data generation unit 370m, and the yellow print data generation unit 370y in the print data generation unit 370 illustrated in FIG. 3 is illustrated. . The print image signal 400 (corresponding to the CMY signal 335 in FIG. 3) is converted into each ink color for printing by the color converter 330 (see FIG. 3).

  The path division table 410 stores division ratios k1, k2, k3, and k4 for dividing into multipaths. The multiplier 420-1 multiplies the print image signal 400 by the division ratio k1 (415-1) of the first pass to calculate the print density of the first pass. The multiplier 420-2 multiplies the print image signal 400 by the division ratio k2 (415-2) of the second pass to calculate the print density of the second pass. The multiplier 420-3 multiplies the print image signal 400 by the division ratio k3 (415-3) for the third pass to calculate the print density for the third pass. The multiplier 420-4 multiplies the print image signal 400 by the division ratio k4 (415-4) of the fourth pass to calculate the print density of the fourth pass.

  First, a signal 430 from the sensor 340 is input to the print data control unit 440. As shown in FIG. 3, the signal 430 is obtained by converting the RGB signal detected by the sensor 340 into the CMY signal 355 by the color conversion unit 350. The print data control unit 440 generates control data used for correcting the density level and generating print data with respect to the signal 430 from the sensor 340 converted into the CMY signal. The signal is transmitted to 450-1 to 450-4.

  The gradation reduction unit 450-1 generates print data for the first pass from the output of the multiplier 420-1 that calculates the print density for the first pass. The gradation reduction unit 450-2 is generated by a print data control unit 440 that generates control data for print data generation from a detection signal from the sensor 340 with respect to the output of the multiplier 420-2 that has calculated the print density of the second pass. Under the control, print data for the second pass is generated. The gradation reduction unit 450-3 is generated by a print data control unit 440 that generates control data for print data generation from a detection signal from the sensor 340 with respect to the output of the multiplier 420-3 that calculates the print density of the third pass. Under the control, print data for the third pass is generated. The gradation reduction unit 450-4 is generated by a print data control unit 440 that generates control data for print data generation from a detection signal from the sensor 340 with respect to the output of the multiplier 420-4 that has calculated the print density of the fourth pass. Under the control, print data for the fourth pass is generated.

  The first-pass print image storage unit 460-1 temporarily stores the output of the gradation reduction unit 450-1 that generated the first-pass print data as a first-pass print image. The second-pass print image storage unit 460-2 temporarily stores the output of the tone reduction unit 450-2 that generated the second-pass print data as a second-pass print image. The third-pass print image storage unit 460-3 temporarily stores the output of the gradation reduction unit 450-3 that generated the third-pass print data as a third-pass print image. The fourth-pass print image storage unit 460-4 temporarily stores the output of the gradation reduction unit 450-4 that generated the fourth-pass print data as a fourth-pass print image.

  Although FIG. 4 illustrates the case of performing four-pass printing, the pass division table 410 determines the print density in each pass. The division ratios k1, k2, k3, and k4 satisfy the relationship represented by 0 <= ki <= 1 (i = 1, 2, 3, 4) and k1 + k2 + k3 + k4 = 1. In the case of four-pass printing, the division ratios k1, k2, k3, and k4 can be set to 0.25 so as to divide evenly into all passes, for example. In addition, k1 = 0.1, k2 = 0.2, k3 = 0.3, so that the printing ratio of the first pass is set low and the printing ratio of the first and subsequent passes is set high. k4 = 0.4 can be set. In this way, by storing the division ratios assuming various scenes in the path division table 410, it is possible to perform pass division at an arbitrary density ratio.

  The print signal converted into each ink color is input to the multiplier 420 and multiplied by the division ratios k1, k2, k3, and k4 read from the pass division table 410 to determine the print density of each pass. Next, a procedure for generating print data for each pass will be described.

  First, when generating print data to be printed in the first pass area, the print image signal 400 separated into each ink color by the color conversion unit 330 (see FIG. 3) is stored in the pass division table 410. The division ratio k1 is multiplied by the multiplier 420-1, and the print density of the first pass is determined. Thereafter, the print density of the first pass is generated by lowering the print density of the first pass by the gradation reducing unit 450-1 of the first pass. The generated first pass print data is stored in the first pass print image storage unit 460-1 as the first pass print image.

  Next, when generating print data to be printed in the area of the second pass, the print image signal 400 of each color is multiplied by the division ratio k2 given by the pass division table 410 and the multiplier 420-2, so that two passes The print density of the eyes is determined. Further, the recording state of the first pass is simultaneously detected by the sensor 340, and based on the signal 430 obtained by converting the detection signal into the CMY signal by the color conversion unit 350 (see FIG. 3), the print data control unit 440 determines the density level. Correction, generation of control data with reduced gradation, and the like are performed. Based on this control data, the print density of the second pass is reduced in gradation by the gradation reduction unit 450-2 in the second pass.

  That is, while the print data of the second pass is simply generated conventionally, the sensor 340 detects the recording state of the print by the previous carriage scan in the multi-pass print (print of the first pass). Thus, the generation of print data (dot generation, dot arrangement, etc.) by the gradation reduction unit 450-2 is to be controlled. The generated second pass print data is stored in the second pass print image storage unit 460-2 as a second pass print image. The generation of print data to be printed in the third and fourth pass areas can be performed in the same manner as the generation of print data to be printed in the second pass area.

  FIG. 5 is a block diagram showing a functional configuration of the gradation reduction unit 450 according to the first embodiment. In this embodiment, the gradation reduction unit 450 performs gradation reduction using an error diffusion method.

  The input image signal 500 corresponds to the output signal of the multiplier 420 shown in FIG. A control signal 505 corresponds to an output signal of the print data control unit 440 shown in FIG. 4 and is a signal for controlling the gradation reduction unit 450.

  The adder 510 adds an error signal 575 indicating a quantization error to the input image signal 500, and outputs a signal 515 with the quantization error added. The threshold generation unit 520 generates a threshold for performing quantization based on the input control signal 505, and outputs the generated threshold to the quantizer 530. The quantizer 530 quantizes the input image signal 515 including an error based on the threshold value input from the threshold value generation unit 520 to reduce the gradation, and outputs an output signal 535.

  The inverse quantizer 550 inversely quantizes the output signal 535 whose gradation has been reduced based on the evaluation value 540. The adder 560 calculates an error resulting from the quantization of the input image signal 515 including the error, and outputs a quantization error signal 565. The diffusion / collection unit 570 performs diffusion or collection based on the quantization error signal 565 and outputs an error signal 575. The diffusion / collection unit 570 is connected to an error buffer 580 that temporarily stores a quantization error, which is a buffer memory for filling a gap between the processing speed of the CPU and the processing speed of the printer or the like.

  Normally, a constant is used as the threshold value generated by the threshold value generation unit 520, and binarization is performed by the quantizer 530 while performing error diffusion on the input image signal 500. On the other hand, in this embodiment, a variable is used to correct a texture or a delay in dot formation.

  As shown in FIG. 4, the control signal 505 input to the threshold value generation unit 520 is a control in which a signal 430 indicating the print state detected by the sensor 340 is generated as a signal for controlling print data by the print data control unit 440. Corresponds to data. Accordingly, since the threshold value is changed according to the printing state detected by the sensor 340, it is possible to control data generation in the error diffusion processing so as to make the printing density uniform.

  That is, the printing state in which the sensor is printed on the print medium 200 by the printer engine unit 180 by the scanning motion one time before the noted scanning motion in at least one scanning motion among the plural scanning motions. And the threshold value is changed based on the detection result. Thus, control is performed so that newly formed dots are formed at positions away from the already printed dots.

  For example, in order to perform quantization on a position where dots have already been formed or a position where the density has increased due to the concentrated formation of dots based on the print state detected by the sensor until the previous scan. The threshold value is changed to a higher value to control dot formation. On the other hand, in a region where dots are not formed or a region where the print density is low, the threshold value for performing quantization is changed to a low value, and control is performed so as to promote dot formation.

  By controlling the threshold in this way, it is possible to improve the dispersibility of dots between passes in multipass printing. As a result, in order to change the threshold value in the gradation reduction process using the error diffusion method, the image signal that has been subjected to pass division based on the division ratio and for which the print density for each pass has been determined is not dot formation rate, By controlling the formation position, density unevenness can be reduced.

  Note that when the print data for the first pass is generated, there is no print data before the first pass, so the print data control unit 440 (see FIG. 4) does not exist. For this reason, no control signal is input, and the threshold value generated by the threshold value generation unit 520 is a fixed value (or a value that is changed to correct the texture and dot formation delay), and normal quantization is performed.

  In the present embodiment, the gradation reduction unit 450 performs the gradation reduction process using the error diffusion method, but the gradation reduction process can also be performed using the dither method. That is, the generation of print data can be controlled by controlling the threshold value of the dither matrix in the same manner as described in the error diffusion process.

  6A is a diagram showing a positional relationship between the print medium 200 and the carriage 210, and FIG. 6B is a diagram showing a print area 205 on the print medium 200 scanned by the carriage 210. FIG.

  An ink jet head 220 and a sensor 230 are mounted on the carriage 210 and can be scanned in both the left and right directions. The sensor 230 is provided on the downstream side in the main scanning direction X with respect to the inkjet head 220. The diffusion matrix 240 is used when the pixel of interest for generating print data and error diffusion are performed.

  The print area 205 is an area where an image is formed by scanning the carriage 210 and ejecting ink from the inkjet head 220. The first pass area 205-1 is an area printed by the inkjet head 220 by scanning the first pass of the carriage 210. The second pass area 205-2 is an area printed by the inkjet head 220 by the second pass scanning of the carriage 210. The third pass area 205-3 is an area printed by the inkjet head 220 by the third pass scanning of the carriage 210. The fourth pass area 205-4 is an area printed by the inkjet head 220 by the fourth pass scanning of the carriage 210.

  The carriage 210 scans the print medium 200 in the main scanning direction X as shown in FIG. At the same time, the sensor 230 detects a state in which printing has been performed by the scan one time before the target scan. Ink is ejected from the ink-jet head 220 onto the print medium 200 by scanning of interest.

  The sensor 230 is a line sensor having the same width as the width of the inkjet head 220 in the sub-scanning direction Y or the same width as the width excluding the nozzle area for printing the first pass. A sensor 230 disposed at a position preceding the inkjet head 220 with respect to the main scanning direction X of the carriage 210 indicates a print state on the print medium 200 printed in the previous scan according to the main scanning direction X of the carriage 210. To detect.

  The print state detected by the sensor 230 is read in the line direction because the sensor 230 is a line sensor. The detection signal read from the sensor 230 is read in the vertical direction (vertical direction in the figure) with respect to the print area 205 of the current scan. In synchronization with this processing, the input image to be printed temporarily stored in the RAM 120 (see FIG. 1) of the printer 10 is read in the vertical direction (vertical direction in the figure) with respect to the print area 205 of the current scan. .

  In this way, the input image signal to be printed read out from the RAM 120 moves the pixel of interest and the diffusion matrix 240 for generating print data in the vertical direction, and controls according to the print state detected by the sensor 230. Print data is generated. The generated print data is stored in the memory.

  Here, the capacity of the memory is regulated by the distance between the sensor 230 and the inkjet head 220. For example, when the sensor 230 is disposed adjacent to the inkjet head 220, the memory capacity is reduced. On the other hand, the place where the sensor 230 can be arranged is limited by the structure of the sensor 230, the inkjet head 220, and the carriage 210. The memory capacity of the print data depends on this positional relationship.

  Also, the print data is generated in the vertical direction in the print area 205 by the current scan. For this reason, print data is generated while vertically cutting the print area 205 by the current scan from the first pass area 205-1 to the fourth pass area 205-4. For this reason, the multiplier 420, the gradation reduction unit 450, and the print image storage unit 460 (see FIG. 4) do not need to be provided independently for each color, and only one is provided for all colors. Can be done.

  16A to 16D are diagrams showing the positions of dots formed in each pass. When density unevenness occurs in multi-pass printing, the printing state up to the previous scan is detected by a sensor, and dot formation control is performed based on the detection result.

  First, as shown in FIG. 16A, the first pass is printed. Next, the printing medium is conveyed, and the second pass printing is performed as shown in FIG. When printing the second pass, the print state of the first pass is detected by a sensor. The print state means, for example, variations in the ejection direction of the ink jet head at the time of printing in the first pass, the transport amount when the print medium is transported after the completion of printing in the first pass, and the like.

  The generation of print data corresponding to a print process to be performed from now is controlled based on the result detected by the sensor. For example, as shown in FIG. 16B, it is possible to detect a state in which the amount of conveyance of the print medium at the end of the first pass printing is larger than the reference value. Further, it is possible to detect a state in which the ejection direction of the nozzles of the third line (the center line in the upper and lower three rows shown in FIG. 16A) printed in the first pass is shifted upward. In this way, data to be printed in the second pass is generated based on the detected printing state in the first pass.

  For this reason, the printing dot (indicated by reference numeral 2 in the circle) of the second pass is larger than that of the conventional case where the printing dot is formed as shown in FIG. The dot 2 is indicated in the circle), and the print dot formation position (nozzle ejection direction, etc.) is corrected to generate print data. Then, as shown in FIG. 16B, the second pass printing is performed.

  Next, after the printing of the second pass is completed, the print medium is conveyed, and the printing state in which the printing in the first and second passes is detected by the sensor, and based on the detected result, the third pass Print data is generated. As a result, printing dots (indicated by reference numeral 3 in a thick circle) are printed by correcting the printing dot formation position (nozzle ejection direction, etc.) as compared with the conventional case of forming printing dots. Generate data. Then, as shown in FIG. 16C, the third pass printing is performed.

  Similarly, after the printing of the third pass is completed, the print medium is conveyed, and the printing state in which the printing in the first to third passes is detected by the sensor, and based on the detected result, the fourth pass Print data is generated. Based on the generated print data for the fourth pass, as shown in FIG. 16D, the fourth pass is printed, and an image is formed on the print medium. Compared with the image in which nothing is controlled as shown in FIG. 15, it can be confirmed that density unevenness is clearly reduced in FIG.

  Therefore, the print dot formation position for each print scanning movement can be corrected by detecting the print state of the previous scan with the sensor and generating print data based on the detection result. As a result, when multi-pass printing is performed, even if variations occur in the characteristics of the inkjet head, the conveyance amount of the print medium, etc., dots between each pass can be evenly distributed, resulting in density unevenness. Can be reduced.

[Modification 1 of the first embodiment]
FIG. 7 is a block diagram illustrating a functional configuration of the print data generation unit 370 according to the first modification of the first embodiment.

  The multiplier 420 divides the print image signal 400 by density based on the input from the path division table 410. The print data control unit 440 controls the print data based on the signal 430 detected by the sensor 340 for the print image of each pass divided by the multiplier 420. The gradation reduction unit 450 receives the control of the print data control unit 440 and reduces the gradation of the print data divided by the multiplier 420. The print image storage unit 460 stores the print data of each pass that has been subjected to gradation reduction by the gradation reduction unit 450.

  The print image signal 400 converted into the CMY signal and the signal 430 detected by the sensor 340 and converted into the CMY signal, as shown in FIG. 6, cause the carriage 210 to scan the print area 205 in the vertical direction. Control. In the print image signal 400, division ratios k1, k2, k3, and k4 corresponding to the print area 205 of each pass are read from the pass division table 410, and the print density corresponding to the print area 205 of each pass is obtained by the multiplier 420. Is multiplied. Based on the signal 430 output from the sensor 340, the print data control unit 440 corrects the density level, generates control data, and the like. Based on the result, the gradation reduction unit 450 applies each pass. Corresponding print data is generated. The generated print data is temporarily stored in the print image storage unit 460 and printed on a print medium by the print control unit 380 (see FIG. 3) to form an image. At this time, the first pass area 205-1 (see FIG. 6) formed on the print medium has not been printed in the previous pass and there is no signal from the sensor 340. The print density input without being controlled by the gradation unit 450 is directly reduced in gradation.

[Modification 2 of the first embodiment]
In the first embodiment described above, an RGB pure color filter is used as the sensor 342. However, a CMY complementary color filter can also be used as in this modification.

  FIG. 8 is a block diagram illustrating a functional configuration of an image forming apparatus according to Modification 2 of the first embodiment. FIG. 14 is a diagram illustrating the positions of dots formed in each pass in Modification 2 of the first embodiment. Note that the circles in FIG. 14 indicate dots formed on the print medium, and the numbers 1, 2, 3, and 4 in the circles indicate scanning numbers on which dots are formed.

  In this case, the print state detected by the sensor 342 is not RGB signals as shown in FIG. 3, but CMY signals indicated by signals C ′, M ′, and Y ′ as shown in FIG. Input to the unit 352. The color conversion unit 352 converts the ink color to a CMY signal based on the signals C ′, M ′, and Y ′ input from the sensor 342. Thereby, even if a CMY complementary color filter is used as the sensor 342, the same effect can be obtained.

<Second Embodiment>
In the first embodiment described above, the dot position is controlled based on the printing state detected by the sensor, but in this embodiment, the printing density is corrected based on the printing state detected by the sensor. Is different. Note that these embodiments may be implemented alone or in combination. Moreover, about the structure similar to the above-mentioned 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 3, the input image 320 to be printed is converted into a CMY signal for printing by the printer 10 (see FIG. 1) by the color conversion unit 330 and input to the print data generation unit 370 for each color. The Similarly, the signal detected by the sensor 340 for detecting the print state is converted into a CMY signal by the color conversion unit 350 and input to the print data generation unit 370 for each color.

  The print data generation unit 370 corrects the recording density ratio for each print scanning movement in units of nozzles based on the print state detected by the sensor 340. In other words, the print data generation unit 370 corrects the density level of the input image 320 based on the signal detected by the sensor 340 and converted into the CMY signal by the color conversion unit 350.

  FIG. 9 is a block diagram illustrating a functional configuration of the print data generation unit 370 according to the second embodiment. Here, the functional configuration of one of the cyan print data generation unit 370c, the magenta print data generation unit 370m, and the yellow print data generation unit 370y in the print data generation unit 370 illustrated in FIG. 3 is illustrated. .

  The density converter 600 converts the print density into a print density based on the signal 430 detected by the sensor 340.

  The path division table 610 stores division ratios k1, k2, k3, and k4 for dividing into multipaths. The multiplier 620-1 multiplies the print image signal 400 by the division ratio k1 (615-1) for the first pass. The multiplier 620-2 multiplies the print image signal 400 by the sum of the division ratios of the first and second passes k1 + k2 (615-2). The multiplier 620-3 multiplies the print image signal 400 by the total division ratio k1 + k2 + k3 (615-3) of the first to third passes.

  Adder 630-1 calculates the difference between the print density of the first pass calculated by multiplier 620-1 and the print density detected by sensor 340. The adder 630-2 calculates a difference between the total print density of the first and second passes calculated by the multiplier 620-2 and the print density detected by the sensor 340. The adder 630-3 calculates the difference between the total print density of the first to third passes calculated by the multiplier 620-3 and the print density detected by the sensor 340.

  The adder 640-2 adds the difference between the print density of the first pass and the print density detected by the sensor 340 (the output result of the adder 630-1) to the print density of the second pass. The adder 640-3 adds the difference (the output result of the adder 630-2) between the total print density of the first and second passes and the print density detected by the sensor 340 to the print pass of the third pass. The adder 640-4 adds the difference (the output result of the adder 630-3) between the total print density of the first to third passes and the print density detected by the sensor 340 to the print pass of the fourth pass.

  The gradation reduction unit 650-1 generates print data for the first pass based on the output of the multiplier 420-1 that has calculated the print density for the first pass. The gradation reduction unit 650-2 generates print data for the second pass based on the output of the adder 640-2 that calculates the print density for the second pass. The gradation reduction unit 650-3 generates print data for the third pass based on the output of the adder 640-3 that calculates the print density for the third pass. The gradation reduction unit 650-4 generates print data for the fourth pass based on the output of the adder 640-4 that calculates the print density for the fourth pass.

  Here, in the present embodiment, for the print image signal 400, the cumulative density calculated by the multiplier 420 for the division ratio of each pass is expressed as the target output density of each pass. This is not the density of the result printed on the print medium, but the term “print density” is used as a value to be handled in processing.

  First, the print image signal converted into each ink color is input to a multiplier 420 that calculates a print density for each pass, and multiplied by division ratios k1, k2, k3, and k4 read from the pass division table 410. Then, the target output density of each pass is calculated.

  When generating print data for the first pass, the print density for the first pass is calculated by the multiplier 420-1, and the print data is generated by the gradation reduction unit 650-1, as in the first embodiment. Generated and stored in the first pass print image storage unit 460-1.

  When generating the print data for the second and subsequent passes, the multiplier 420 calculates the print density of each pass, and at the same time, the multiplier 620 calculates the target output density of the previous scan.

  When printing the second pass, the target output density of the first pass is calculated in the print image signal 400 and the division ratio k1 of the first pass is calculated by the multiplier 620-1. On the other hand, the signal indicating the print state detected by the sensor 340 is color-converted into a CMY signal, and then converted into a detected density by the density converter 600. The detected density in the first pass is input to the adder (subtractor) 630-1 together with the output of the multiplier 620-1 in order to calculate a difference by comparison with the calculated target output density. The difference between the target output density of the first pass calculated by the adder 630-1 and the detected density is added to the print density of the second pass by the adder 640-2. The print density of the second pass corrected by the difference between the target output density of the first pass and the detected print density is generated by the gradation reduction unit 650-2, and the generated second pass is generated. The print data is stored in the second pass print image storage unit 460-2 as the second pass print image.

  Further, when printing the third pass, the print density of the third pass is calculated by the multiplier 420-3, and at the same time, the total target output density of the first and second passes already printed is printed. Multiplier 620-2 multiplies signal 400 by the sum of the division ratios of the first and second passes, k1 + k2. On the other hand, based on the printing state detected by the sensor 340, the detected density after the second pass printing is converted by the density converter 600. The difference between the target output density after printing in the second pass calculated by the multiplier 620-2 and the detected density detected by the sensor 340 is calculated by the adder 630-2, and the adder is added to the print density in the third pass. It is added at 640-3. The print density of the third pass corrected by the difference between the target output density after the second pass printing and the detected print density is generated by the tone reduction unit 650-3, and the generated 3 The print data of the pass is stored in the third pass print image storage unit 460-3 as the third pass print image.

  When printing the fourth pass, the print density of the fourth pass is calculated by the multiplier 420-4, and at the same time, the total target output density of the first to third passes already printed is used as the print image signal 400. On the other hand, a multiplier 620-3 that multiplies the sum of the division ratios of the first to third passes. On the other hand, based on the printing state detected by the sensor 340, the detected density after the third pass printing is converted by the density conversion unit 600. The difference between the target output density after printing for the third pass calculated by the multiplier 620-3 and the detected density detected by the sensor 340 is calculated by the adder 630-3 and added to the printing density for the third pass. It is added at 640-4. For the print density of the fourth pass corrected by the difference between the target output density after the third pass printing and the detected print density, print data is generated by the gradation reduction unit 650-4 and generated 4 The pass print data is stored in the fourth pass print image storage unit 460-4 as a fourth pass print image.

  Therefore, the print data generation unit 370 is to accumulate the print data to be printed on the print medium up to the print scan motion one time before the print scan motion in at least one print scan motion among the multiple print scan motions. It functions as a cumulative density calculator that calculates density. The print data generation unit 370 functions as a difference calculation unit that calculates a difference between the cumulative density calculated by the cumulative density calculation unit and the density detected by the sensor. Thereby, the print data generation unit 370 corrects the print data after the noted recording scanning motion so that the difference calculated by the difference calculation unit becomes zero.

  In this manner, the print data stored in the print image storage unit 460 forms an image on the print medium by driving the ink jet head by the print control unit 380 (see FIG. 3).

  In this embodiment, the configuration of the image forming apparatus is the same as that of the first embodiment (see FIG. 3), and the processing after color separation into CMY signals that are ink colors is shown in FIG. The sensor 340 detects the print state, detects the print density of the print result obtained by the previous scan, calculates the difference (that is, the density error) from the target output density that should be printed, and determines the density error. Only, the print data is generated so as to be corrected in the next scan printing. For this reason, instead of color-converting the detection signal detected by the sensor into CMY ink colors, color conversion is performed to an ideal CMY system for image formation, and the density of the ideal CMY color space. An error may be calculated and corrected to print data. As a result, correction can be made even when the calculated color conversion differs from the color of the image formed on the print medium depending on the combination of the ink and the print medium.

[Modification 1 of Second Embodiment]
FIG. 10 is a block diagram illustrating a functional configuration of the print data generation unit 370 according to the first modification of the second embodiment.

  Multiplier 420 divides the print image signal 400 in density for each pass based on the input from the pass division table 610. Multiplier 620 multiplies print image signal 400 and the accumulated value to calculate a target output density. Adder 630 calculates the difference between the target output density calculated by multiplier 620 and the density detected by sensor 340 and converted by density converter 600. The adder 640 adds the difference calculated by the adder 630 to the print density of each pass. The gradation reduction unit 650 reduces the gradation of the print image of each pass to which the difference is added by the adder 640, and generates print data. The print image storage unit 460 stores the print data of each pass subjected to the gradation reduction by the gradation reduction unit 650.

  The print image signal 400 converted into the CMY signal and the signal 430 detected by the sensor 340 and converted into the CMY signal, as shown in FIG. 6, cause the carriage 210 to scan the print area 205 in the vertical direction. Control. In the print image signal 400, the division ratios k 1, k 2, k 3, and k 4 corresponding to the print area 205 (see FIG. 6) of each pass are read from the pass division table 610, and the multiplier 420 corresponds to the print area 205. The print density is multiplied. At the same time, after the second pass, from the pass division table 610, if the target scan is the n-th pass, the total of the division ratios up to the (n-1) -th pass, which is the first scan before the n-th pass ( Calculated by the following equation), and the multiplier 620 calculates the target output density.

これにより、ｎパス目を印字する際に、ｎ−１パス目までの合計の目標出力濃度を算出する。

Thereby, when printing the n-th pass, the total target output density up to the (n-1) -th pass is calculated.

  On the other hand, the signal 430 detected by the sensor 340 is converted into a detected density by the density converter 600, and the adder 630 calculates the difference between the target output density and the detected density. The calculated difference is corrected to the print density of each pass by the adder 640, and print data corresponding to each pass is generated by the gradation reduction unit 650. The generated print data is temporarily stored in the print image storage unit 460 and printed on a print medium by the print control unit to form an image.

  As described above, according to the present embodiment, in the second and subsequent passes of multi-pass printing, the difference between the target output density by the previous scan and the detected density detected by the sensor 340 is determined for the next printing. Thus, density unevenness can be more reliably reduced. That is, when a density error occurs due to variations in the characteristics of the inkjet head, the conveyance amount of the print medium, etc., the density printed in the previous scan is detected by the sensor 340 in the second and subsequent scans. Then, the difference between the detected density and the target output density to be printed (that is, the generated density error) is calculated, and the density unevenness is corrected by correcting the print data in the pass so as to eliminate the calculated difference. Can be more reliably reduced.

<Third Embodiment>
FIG. 11 is a block diagram illustrating a functional configuration of the print data generation unit 370 according to the third embodiment. In the first embodiment (see FIG. 3), after the input image 320 to be printed is converted into a CMY signal for printing with an inkjet printer by the color conversion unit 330, the signal detected by the sensor 340 is also converted to the color conversion unit 350. Are converted into CMY signals and input to the print data generation unit for each color. In the print data generation unit, density level correction and the like are performed using a signal detected by the sensor 340 and converted into a CMY signal by the color conversion unit 350. The input image signal 320 and the signal detected by the sensor 340 are converted into CMY signals by the color conversion units 330 and 350, respectively, and input to the print data generation unit 370, respectively. In addition, about the structure similar to the above-mentioned 2nd Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted. In the present embodiment, the description will focus on differences from the configuration of the print data generation unit 370 shown in FIG. 9 of the second embodiment.

  The pass division table 612 stores the accumulated density (target output density) up to each scan when dividing into multi-passes. The multiplier 425-1 multiplies the print image signal 400 by the first pass division ratio k1 (417-1). The multiplier 425-2 multiplies the print image signal 400 by the total division ratio k1 + k2 (417-2) of the first and second passes to calculate the cumulative density up to the second pass. The multiplier 425-3 multiplies the print image signal 400 by the total division ratio k1 + k2 + k3 (417-3) of the first to third passes to calculate the cumulative density up to the third pass.

  The adder 645-2 calculates the cumulative density (target output density after the second pass printing) to be printed by the second pass calculated by the multiplier 425-2 and the first pass print density detected by the sensor. Is calculated to calculate the print density of the second pass. The adder 645-3 prints the cumulative density (target output density after the third pass printing) to be printed by the third pass calculated by the multiplier 425-3 and the first and second pass prints detected by the sensor. The difference between the print density and the print density is calculated to calculate the print density in the third pass. The adder 645-4 calculates the difference between the cumulative density to be printed before the final pass (that is, the target output density of the final pass) and the print density by the printing up to the third pass detected by the sensor, and performs four passes. The print density at the eye is calculated.

  The gradation reduction unit 650-1 generates print data for the first pass from the output of the multiplier 420-1 that calculates the print density for the first pass. The gradation reduction unit 650-2 generates print data for the second pass from the output of the adder 640-2 that calculates the print density for the second pass. The gradation reduction unit 650-3 generates print data for the third pass from the output of the adder 640-3 that calculates the print density for the third pass. The gradation reduction unit 650-4 generates print data for the fourth pass from the output of the adder 640-4 that calculates the print density for the fourth pass.

  Here, as in the first and second embodiments, of the print data generation unit 370 shown in FIG. 3, the cyan print data generation unit 370c, the magenta print data generation unit 370m, and the yellow print data generation unit 370y. An example of the functional configuration of any one of the colors will be described. In the present embodiment, the accumulated target output density printed up to the pass for printing (n-th pass) and the previous pass (n-1 pass) and the previous scan are printed and detected by the sensor. A difference from the detected density is obtained and the difference density is printed.

  First, the print image signal converted into each ink color is input to a multiplier 425 for calculating the cumulative print density for each pass, and multiplied by coefficients (k1, k1 + k2, k1 + k2 + k3) read from the pass division table 612. The accumulated print density of each pass is determined.

  When generating the print data for the first pass, as in FIG. 4, the print density for the first pass is calculated by the multiplier 425-1, and the print data is generated by the gradation reduction unit 650-1. It is stored in the print image storage unit 460-1 for the first pass.

  When generating the print data for the second pass, the multiplier 425-2 calculates the cumulative print density up to the second pass (the sum of the print densities for the first and second passes). On the other hand, the detection signal detected by the sensor is color-converted into a CMY signal, and then converted into a detected density by the density converter 600. The detected density in the first pass detected by the sensor is compared with the accumulated target output density in the second pass, and the print density in the first and second passes is calculated. Entered. The adder 645-2 calculates the difference between the accumulated target output density of the first and second passes and the print density detected by the sensor after printing the first pass, and prints in the second pass. The concentration to be calculated is calculated. For the calculated print density in the second pass, print data is generated by the gradation reduction unit 650-2, and the generated second pass print data is used as the second pass print image. It is stored in the storage unit 460-2.

  When generating the print data for the third pass, the cumulative print density for the first to third passes is calculated by the multiplier 425-3. On the other hand, the density conversion unit 600 converts the detected density after printing the second pass from the printing state detected by the sensor. The detected density as the printing state printed in the first and second passes detected by the sensor is compared with the accumulated target output density in the first to third passes, and the adder is used to calculate the print density in the third pass. (Subtractor) Input to 645-3. The adder 645-3 calculates the difference between the target output density of the first to third passes and the print density detected by the sensor after printing the second pass, and prints in the third pass. The concentration to be calculated is calculated. For the calculated print density in the third pass, print data is generated by the gradation reduction unit 650-3, and the generated print data in the third pass is the third pass print image. It is stored in the storage unit 460-3.

  When generating print data for the fourth pass, the accumulated print density for the first to fourth passes is the final pass for the fourth pass and the density of the input print image itself. The multiplier 425 for calculating the cumulative print density at is unnecessary. The print status of the first to third passes is detected by the sensor with respect to the target output density in the fourth pass, and the detected print density is compared with the print image, and added to calculate the print density of the fourth pass. Is input to a subtracter 645-4. The adder 645-4 calculates the difference between the print target density (printed image density) of the first to fourth passes and the print density detected by the sensor after the third pass is printed. The density to be printed in the fourth pass is calculated. For the calculated print density in the fourth pass, print data is generated by the gradation reduction unit 650-4, and the generated print data in the fourth pass is the fourth pass print image. It is stored in the storage unit 460-4.

[Modification 1 of the third embodiment]
FIG. 12 is a block diagram illustrating a functional configuration of the print data generation unit 370 according to the first modification of the third embodiment.

  The multiplier 425 multiplies the print image signal 400 by the sum of the division ratios up to the current scan (target output density) to calculate the target output density for the current scan. Adder 645 calculates the difference between the target output density calculated by multiplier 425 and the detected density detected by the sensor. The gradation reduction unit 650 generates print data based on the print image of each pass. The print image storage unit 460 stores the print data of each pass subjected to the gradation reduction by the gradation reduction unit 650.

  The CMY-converted print image signal 400 and the CMY-converted signal 430 detected and read by the sensor are scanned vertically in the print area 205 as shown in FIG. In the print image signal 400, the total (target output density) k 1, k 1 + k 2, k 1 + k 2 + k 3, and 1 of the cumulative division ratios k 1, k 2, k 3, and k 4 corresponding to each pass area are read from the pass division table 612. The coefficient to be read is given by the following equation as the sum of the division ratios of the first to nth passes.

パス分割テーブル６１２で与えられた分割比率と印字画像信号４００は、乗算器４２５で乗算され、パス領域に応じた累積の目標出力濃度が算出される。一方、センサで検出された信号４３０が濃度変換部６００で検出濃度へ変換され、目標出力濃度とそれ以前の走査で印字され、検出された検出濃度との差分が加算器６４５で算出される。算出結果は、現在の走査（ｎパス目）の印字濃度に現在の走査より１回前の走査（ｎ−１パス目）の印字濃度誤差を加算したものであり、印字濃度が補正された結果として、低階調化部６５０で各パスに応じた印字データが生成される。生成された印字データは、印字画像記憶部４６０に一時記憶され、印字制御部３８０（図３参照）で印字媒体に印字され、画像が形成される。

The division ratio given by the pass division table 612 and the print image signal 400 are multiplied by the multiplier 425, and the cumulative target output density corresponding to the pass area is calculated. On the other hand, the signal 430 detected by the sensor is converted to the detected density by the density conversion unit 600, printed by the target output density and the previous scan, and the difference between the detected density detected is calculated by the adder 645. The calculation result is obtained by adding the print density error of the previous scan (n−1 pass) to the print density of the current scan (n pass) and correcting the print density. As a result, the gradation reduction unit 650 generates print data corresponding to each pass. The generated print data is temporarily stored in the print image storage unit 460, and printed on a print medium by the print control unit 380 (see FIG. 3) to form an image.

  As described above, according to the present embodiment, by calculating the difference between the density printed up to the scan before the target pass and the target output density, and correcting the density so as to eliminate the difference. , Density unevenness can be reduced more reliably. That is, it is possible to correct the density unevenness even when a density error occurs due to variations in the characteristics of the inkjet head, the conveyance amount of the print medium, and the like. In addition, since the multiplier and the adder are omitted as compared with the second embodiment, the control circuit can be simplified.

<Fourth Embodiment>
In the first to third embodiments described above, as shown in FIG. 2A, the sensor 230 is disposed at a position preceding the inkjet head in the direction in which the recording scanning movement is performed (main scanning direction X). Then, the generation of print data was controlled using the detection signal of the sensor 230. On the other hand, the present embodiment is different in that the sensor 230 is disposed at a position subsequent to the ink jet head. In addition, about the structure similar to the above-mentioned 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  When the sensor 230 is arranged at a position preceding the ink jet head with respect to the main scanning direction X of the carriage, the print state printed by the noticed scan cannot be detected, but it is 1 than the noticed scan. It is possible to detect the printing state up to the previous scan. For this reason, it is possible to detect not only variations in the characteristics of the inkjet head (such as variations in ejection amount and ejection direction) but also a printing state including variations in the conveyance amount of the print medium.

  However, print data is generated based on the print state detected by the sensor 230, and when the inkjet head 220 reaches the position of the detected sensor as the carriage scans, the inkjet head 220 is driven with the generated print data. There is a need to. For this reason, it is necessary to generate print data while detecting a print state with a sensor, and to drive an ink-jet head according to scanning of a carriage, instead of print control using a band memory generally performed conventionally. is there. Here, the print control using the band memory means that all print data generation is completed and stored in the band memory before the carriage scan, and the print control unit drives the inkjet head in synchronization with the carriage scan. In this case, the image is formed by discharging. For this reason, the direction in which the print data is generated is shown in FIG. 6 and has already been described.

  On the other hand, as shown in FIG. 2B, in the present embodiment, the case where the sensor 230 is arranged at a position subsequent to the inkjet head 220 in the main scanning direction X will be described.

FIG. 13 is a block diagram illustrating a functional configuration of an image forming apparatus according to the fourth embodiment.
The memory 360c temporarily stores a cyan signal obtained by converting the print state detected by the sensor 340 into an ink color CMY signal by the color conversion unit 350. The memory 360m temporarily stores a magenta signal obtained by converting the print state detected by the sensor 340 into an ink color CMY signal by the color conversion unit 350. The memory 360y temporarily stores a yellow signal obtained by converting the print state detected by the sensor 340 into an ink color CMY signal by the color conversion unit 350.

  In the present embodiment, as described above, since the sensor 340 is provided on the upstream side of the ink jet head 220 (see FIG. 2), the printing state is detected by the sensor 340 immediately after printing by the ink jet head 220 is performed.

  A print state detection signal detected by the sensor 340 is converted into a CMY signal 355 that is an ink color by a color conversion unit 350. The CMY signal 355 is temporarily stored in the memory 360 (cyan memory 360c, magenta memory 360m, yellow memory 360y). The detection signal stored in the memory 360 is input to the print data generation unit 370 together with the print image signal converted from the input image signal 320 into the ink color CMY signal 335 by the color conversion unit 330, and print data is generated. .

  As described above, according to the present embodiment, it is not necessary to perform real-time detection of the print state by the sensor, generation of print data, and printing by the inkjet head while scanning the carriage. For this reason, these processes can be performed separately. Further, since print data is not generated in real time as the carriage scans, it is not necessary to generate print data in the nozzle array direction of the inkjet head as shown in FIG. The print data can be generated in the main scanning direction. As a result, the hardware is less likely to be a restriction on print data generation (timing, latency for error memory access, etc.). Can be controlled.

  Therefore, the present invention can be applied to an embodiment in which print data is generated prior to carriage scanning and printing is performed based on the print data stored in the band memory.

<Other embodiments>
Note that the present embodiment can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), and a device (for example, a copier, a multifunction peripheral, The present invention may be applied to a facsimile machine or the like.

  Further, the present invention may supply a computer-readable storage medium (or recording medium) that stores a computer program code of software that implements the functions of the above-described embodiments to a system or apparatus. Further, the present invention may be applied to the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium recording the program code constitutes the present embodiment. In addition, an operating system (OS) or the like running on the computer performs part or all of the actual processing based on the instruction of the program code, and the functions of the above-described embodiments may be realized by the processing. Needless to say, it is included.

  Further, the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer. Then, based on the instruction of the program code, the CPU or the like provided in the function expansion card or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. It goes without saying that it is included in the invention.

  When the present embodiment is applied to the above-described computer-readable storage medium, the storage medium stores computer program codes corresponding to the above-described flowcharts and functional configurations.

  Note that the sensor length, arrangement method, number of path divisions, path division ratio, and the like shown in the first to fourth embodiments are only one embodiment, and are the constituent features of the present invention. It is not limited.

1 is a block diagram illustrating a functional configuration of a printer according to a first embodiment of the present invention. (A) thru | or (c) is a figure which shows the arrangement | positioning state of the printing medium 200 and the carriage 210. FIG. 1 is a block diagram illustrating a functional configuration of an image forming apparatus according to a first embodiment. 3 is a block diagram illustrating a functional configuration of a print data generation unit 370 according to the first embodiment. FIG. It is a block diagram which shows the functional structure of the gradation reduction part 450 which concerns on 1st Embodiment. (A) is a diagram showing a positional relationship between the print medium 200 and the carriage 210, and (b) is a diagram showing a print area 205 on the print medium 200 scanned by the carriage 210. FIG. It is a block diagram which shows the functional structure of the print data production | generation part 370 which concerns on the modification 1 of 1st Embodiment. FIG. 10 is a block diagram illustrating a functional configuration of an image forming apparatus according to a second modification of the first embodiment. It is a block diagram which shows the functional structure of the print data generation part 370 which concerns on 2nd Embodiment. It is a block diagram which shows the functional structure of the print data generation part 370 which concerns on the modification 1 of 2nd Embodiment. It is a block diagram which shows the functional structure of the print data generation part 370 which concerns on 3rd Embodiment. It is a block diagram which shows the functional structure of the print data generation part 370 which concerns on the modification 1 of 3rd Embodiment. FIG. 10 is a block diagram illustrating a functional configuration of an image forming apparatus according to a fourth embodiment. It is a figure which shows the position of the dot formed in each pass in the prior art example and the modification 2 of 1st Embodiment. It is a figure which shows the position of the dot formed by each pass in a prior art example. (A) thru | or (d) is a figure which shows the position of the dot formed in each pass in 1st Embodiment. It is a figure which shows the prior art example of multipass printing.

Explanation of symbols

10 Printer 20 Personal Computer 30 Digital Camera 100 CPU
110 ROM
120 RAM
130 USB Device Interface 140 USB Host Interface 150 Image Processing Unit 160 Print Control Unit 170 Drive Control Unit 180 Printer Engine Unit 200 Print Medium 210 Carriage 220 Inkjet Head 220c Cyan Head 220m Magenta Head 220y Yellow Head 220bk Black Head 230 Sensor 320 Input Image 330 Color Conversion Unit 335 CMY Signal 335c Cyan Signal 335m Magenta Signal 335y Yellow Signal 340 Sensor 350 Color Conversion Unit 370 Print Data Generation Unit 370c Cyan Print Data Generation Unit 370m Magenta Print Data Generation Unit 370y For Yellow Print data generator 380 Print controller 380c Cyan print controller 380m Magenta print controller 380y Yellow Use the print controller 400 print the image signals 410 pass division table 415-1 first pass dividing ratio k1
415-2 Second pass division ratio k2
415-3 Third pass division ratio k3
415-4 Fourth pass division ratio k4
420 Multiplier 420-1 First Pass Multiplier 420-2 Second Pass Multiplier 420-3 Third Pass Multiplier 420-4 Fourth Pass Multiplier 430 CMY Signal 440 Print Data Control Unit 450 Tone Reduction Unit 450 -1 First pass tone reduction unit 450-2 Second pass tone reduction unit 450-3 Third pass tone reduction unit 450-4 Fourth pass tone reduction unit 460 Print image storage unit 460- 1 First-pass print image storage unit 460-2 Second-pass print image storage unit 460-3 Third-pass print image storage unit 460-4 Fourth-pass print image storage unit

Claims (7)

An image forming apparatus for forming an image on the recording medium by causing the recording head to perform recording scanning N times (N is an integer of 2 or more) with respect to the same area on the recording medium,
Print data generating means for generating print data corresponding to each of the print scans;
Recording means for recording the image on the recording medium based on the recording data generated by the recording data generating means;
Along with the k-th recording scan (k is an integer satisfying 2 ≦ k ≦ N) attached to the recording head, the recording unit performs the recording scanning up to the (k−1) -th recording scan on the recording medium. Detecting means for detecting a recording state of the recorded image;
Control means for controlling at least one image processing in the generation of print data corresponding to the k- th print scan based on the print state detected by the detection means up to (k−1) times;
An image forming apparatus comprising:   The recording data generation means generates recording data corresponding to each of the recording scans by dividing the input image data into each of the recording scans and applying halftone processing to the divided divided image data. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 2, wherein the control unit controls the halftone processing by the recording data generation unit.   The image forming apparatus according to claim 1, wherein the control unit corrects a density indicated by the recording data. The density indicated by the recording state of the image recorded on the recording medium by the recording scanning up to (k-1) th by the recording means detected by the detecting means, and the recording scanning up to (k-1) th. A calculation means for calculating a difference between the total density of the corresponding recording data and
The image forming apparatus according to claim 4, wherein the control unit corrects the density indicated by the recording data based on the difference. By computer provided in the image forming apparatus executes reading, the computer program for causing to function the image forming apparatus as an image forming apparatus according to any one of claims 1 to 5. An image forming method executed by an image forming apparatus that forms an image on a recording medium by causing a recording head to perform recording scanning N times (N is an integer of 2 or more) with respect to the same area on the recording medium,
A recording data generating step for generating recording data corresponding to each of the recording scans;
A recording unit for recording the image on the recording medium based on the recording data generated in the recording data generating step;
Including
The recording data generation step includes
Using the detection means attached to the recording head, the recording scanning up to the (k−1) th recording time by the recording means is performed together with the recording scanning of the kth time (k is an integer satisfying 2 ≦ k ≦ N) by the recording means. A detection step of detecting a recording state of an image recorded on the recording medium by:
A control step of controlling at least one image processing in the generation of print data corresponding to the k- th print scan, based on the print state detected by the detection step up to (k−1) times;
An image forming method comprising:

Images